Modern aircraft are frequently equipped with a head-up display (HUD). This system, which is installed in the aircraft flight deck, enables the pilot to monitor the essential parameters of the flight (pitch and roll attitudes, heading, radio-altitude, speed, path, etc.) whilst still observing the exterior during the takeoff phase and in particular during the landing phase.
The head-up control system or display receives the guidance information (heading, attitudes, drift, gradient, etc.) from an inertial unit located in the aircraft hold. On the basis of this information, the head-up control system can display the symbols representing the exterior and the position of the aircraft with respect thereto. These symbols constitute vital information for the pilot when visibility is bad.
In order that the symbols displayed by the head-up control system are correctly superimposed on the exterior or external environment, it is necessary to accurately regulate the orientation of the structure supporting the optical head of said system. This regulation or control, known as harmonization of the head-up control system or display takes place in the factory on a once and for all basis.
More specifically, the regulation of the orientation of the structure supporting the optical head of the head-up control system consists of a regulation in accordance with the longitudinal, lateral and vertical axes of the aircraft.
As in the process described in FR-A-2,632,060, the reference can be the support of the inertial unit, whose three axes can be referenced by the following parameters:
pitch attitude, PA0 roll attitude, PA0 heading (geographical, magnetic, etc.).
In the known regulating process described in FR-A-2,632,060, the pitch and roll attitudes are regulated by attitude gauges. However, the heading of the structure supporting the optical head of the head-up control system or display is regulated by an optical system incorporating a laser, a plane mirror and a prism. The heading of the support structure is regulated by successively orienting the laser beam towards the prism mounted on the inertial unit support placed in the aircraft hold and then towards the mirror installed on the support structure.
However, despite its great simplicity, this process also suffers from certain disadvantages. Thus, its putting into operation makes it necessary to remove the internal lining of the aircraft to enable the laser to be successively oriented towards the prism and then the mirror. Moreover, the aircraft must be placed on a frame and the process is made relatively long and complicated by the fragility of the equipment used. The precision of the settings is also poorly defined and difficult to control.
The invention relates to a novel process for regulating the orientation of a support structure such as that supporting the optical head of a head-up control system or display and which does not suffer from the disadvantages of the known processes, whilst more particularly bringing about a good precision for a relatively short regulation time, no matter what the position of the aircraft and by means of a single procedure for performing the two attitude settings and the heading setting.